Named Oryctodromeus cubicularis ("digging runner of the den"), the newfound species shows that some dinosaurs could live down holes and that they gave extended care to their young, according to a team led by paleontologist David Varricchio of Montana State University in Bozeman.

Digging ability in dinosaurs also suggests they could survive harsher environments than previously thought, the team says.

Details of the find appear in the latest issue of the journal Proceedings of the Royal Society B.

Remains of an adult and two juveniles were first unearthed in 2004 in a fossil den similar in appearance to those of burrowing mammals alive today, the team said.

Numerous smaller tunnels branching from the main den indicated that insects such as bees and possibly mammals also shared the dinosaurs' lair.

Oryctodromeus is described as a swift, two-legged plant-eater that weighed up to 70 pounds (32 kilograms) and measured 6.9 feet (2.1 meters) long.

The width of the dinosaur matched that of its tunnel, which measured some 11.8 inches (30 centimeters) across.

Digging Features

The small dinosaur shows several specializations for burrowing, the team reports, including a modified snout that could be used like a shovel, large bony attachments on its shoulders that held powerful muscles, and strong hips for bracing itself while digging.

The size of the two fossil juveniles indicates that they remained in the den for at least several months, providing some of the best evidence yet for dinosaur parental care, the team said.